The 1.1(1j) & 11.1(1j) release of ACI introduced support for transit routing. Prior to this, the ACI fabric acted as a ‘stub’ routing domain; that is, it was not previously possible to advertise routing information from one routing domain to another through the fabric. I covered L3 Outsides in part 9 of this series where I discussed how to configure a connection to a single routed domain. In this post, we’ll look at a scenario where the fabric is configured with two L3 Outsides and how to advertise routes from one to another. Here is the setup I’m using:

So far in this series, everything we have discussed has been concerned with what happens inside the ACI fabric. At some point however, you will want to connect your fabric to the outside world, either at layer 2 or layer 3. In this part, we’ll take a look at how to set up layer 3 connectivity from ACI to an external router, using a construct called the Layer 3 Outside.

Let’s first take a look at the topology I’m going to discuss in this post: